The Benefits of a Variable Frequency Drive

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Commercial HVAC systems often operate on three phase power, as a standard method of alternating current electric power generation, transmission and distribution. Most conventional building HVAC applications are designed to operate the equipment at a constant speed. That being said, building loads aren’t constant and motors have to perform at full load at any given time. The technology itself controls the speed of a motor, converting incoming AC power to DC and then back to quasi-sinusoidal AC power using an inverter switching circuit, giving the advantage of more speed control.

Variable Frequency Drive is found to be very effective in assisting with energy management for HVAC systems. The main objective of this technology is to ensure that the motor only generates enough energy to power the compressor and no more. VFD provides constant load-matching capacity which results in the elimination of over-capacity running. Recently studied, current variable frequency drive benefits goes beyond the advantage of energy savings or energy efficiency. In conventional common application, the installation of variable frequency drive saves about 35% to 50% energy used by matching system capacity to the actual load.

In addition to energy savings, the equipment would benefit from savings on maintenance costs and enhanced motor lifetime. Installation of VFD applies low frequency and voltage to motors with controlled uprate, reducing vibration and motor wear which significantly contributes to longevity of the motor. Since VFD reduces the speed of compressors to match the need for performance, less mechanical stress is also applied to the component helping to reduce the chance of component failure.

VFD also affects starting currents, lowering a substantial amount of it without affecting the starting torque which would benefit the grid to affect less stress when the motors are powered up. With this capability, failure of electrical equipment can be reduced.

References:

http://blog.parker.com/5-reasons-to-control-your-compressor-with-a-variable-frequency-drive

http://hpac.com/motors-drives/applying-vfds-refrigeration-systems

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